Problem with Json output, content is invalid

Hi!

I'm trying to read some record from the database and create a Json file in output. If I extract only one record the content is valid but if I want to extract, for example, 3 records the content of the file is invalid. I try to validated the Json file on 2 sites and the the response is negative, the content of file is invalid.
Someone have the same problem or I'm doing something wrong?

Thanks!